This invention relates to switch assemblies adapted to be touch activated, and in one aspect to a switch assembly adapted for activation upon use of a door latch.
My aforementioned pending U.S. application Ser. No. 470,537 (the disclosure whereof is incorporated by reference herein and of which this application is a continuation-in-part) discloses a switch assembly particularly adapted to activate an entry light of a building for a predetermined period of time when a person makes contact with the latch on a door in the entryway (e.g. when the person contacts the door knob with his bare or gloved hand, or inserts his key in the lock). The entry light is activated prior to the operation of the door latch to provide a convenience for authorized persons leaving or entering the building, and a deterrent to unauthorized persons prior to their having gained access to the building.
The switch assembly disclosed in my earlier application includes: (1) switch means which is adapted for being switched from a first state to a second state when a triggering signal having an intensity above a predetermined level is applied at an input to the switch means; and (2) a network coupled to the input to the switch means and adapted to electrically couple the switch means to a touch plate (such as a door latch). At the touch plate, there is an incoming signal comprising a continuously received alternating electrical noise component which may be of constant or slowly changing amplitude depending upon ambient conditions at the touch plate. The incoming signal is instantaneously increased when an individual contacts the touch plate. The network includes means for compensating for environmental changes to preclude false alarms by the switch being actuated by a noise signal, and for providing a triggering signal exceeding the predetermined level to switch the switch means when the incoming signal is increased by an individual contacting the touch plate.
In the switch assembly taught in my earlier application, however, the network between the touch plate and the input to the switch means couples the continuous electrical noise component to the input to the switch means, and includes a sensitivity adjust network which applies a bias voltage at the input to the switch means through a special control. The special control is manually adjusted to provide a bias voltage which prevents the electrical noise component from activating the switch means while allowing the increase in the incoming signal caused by an individual contacting the touch plate to cause a triggering signal exceeding the predetermined level, thereby operating the switch means. One should readjust the special control when atmospheric conditions change, since such atmospheric changes will alter the change in the incoming signal produced by an individual contacting the touch plate and the intensity of the electrical noise component. Otherwise, the combination of a previously established bias level from the special control, and an increased electrical noise component (such as may be received at the touch plate during a thunderstorm) may exceed the predetermined level and activate the switch means without an individual contacting the touch plate. Conversely, when atmospheric conditions change to decrease the change in the incoming signal produced by an individual contacting the touch plate (and the level of the electrical noise component received by the switch assembly), the combined effect of a previously established bias level from the special control and the change in the incoming signal produced when an individual contacts the touch plate may not produce the triggering signal required to exceed the predetermined level and switch the switch means.